Blood pump having a magnetically suspended rotor

ABSTRACT

A blood pump preferably has a magnetically suspended rotor that rotates within a housing. The rotor may rotate about a stator disposed within the housing. Radial magnetic bearings may be defined within the stator and the rotor in order to suspend the rotor. The radial magnetic bearings may be passive magnetic bearings that include permanent magnets disposed within the stator and the rotor or active magnetic bearings. The pump may further include an axial magnetic bearing that may be either a passive or an active magnetic bearing. A motor that drives the rotor may be disposed within the housing in order to more easily dissipate heat generated by the motor. A primary flow path is defined between the rotor and the stator, and a secondary flow path is defined between the stator and the rotor. Preferably, a substantial majority of blood passes through the primary flow path. The secondary flow path is large enough so that it provides adequate flushing of the secondary flow path while being small enough to permit efficient operation of the radial magnet bearings across the secondary flow path.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. Application Ser. No.09/356,662 filed on Jul. 19, 1999, now U.S. Pat. No. 6,244,835 entitled“Blood Pump Having A Magnetically Suspended Rotor”, which is acontinuation-in-part application of U.S. patent application Ser. No.08/673,627 filed on Jun. 26, 1996, now U.S. Pat. No. 6,015,272 entitled“Magnetically Suspended Miniature Fluid Pump And Method of Making TheSame,” and claims priority under 35 U.S.C. §119(e) to provisional patentapplication Ser. No. 60/142,354, filed on Jul. 1, 1999, entitled “AnImproved Blood Pump Having A Magnetically Suspended Rotor,” and herebyclaims the benefit of the filing dates of these applications andincorporates by reference theses applications in their entireties.

STATEMENT OF GOVERNMENT RIGHTS

The invention described herein was jointly made by employees of theUnited States Government and by employees of University of Pittsburgh,and it may be manufactured and used by or for the United StatesGovernment for United States Government purposes without payment ofroyalties thereon or therefore.

FIELD OF THE INVENTIONS

This invention relates to blood pumps that have a magnetically suspendedrotor and methods of making the same. This invention also includes bloodpumps that have a housing, a rotor, a stator member attached to thehousing, a means for levitating the rotor such that the rotor issubstantially centered within the housing, and means for rotating therotor. This invention further includes blood pumps that have a geometricconfiguration that minimizes shear stresses on the blood, enhancesbiocompatibility and prevents activation of blood platelets, and therebyprevents thrombosis.

BACKGROUND OF THE INVENTION

The use of rotary pump ventricular assist devices for aiding a patient'sheart in pumping blood is well known. Such rotary pump ventricularassist devices may be connected to a patient's heart in aleft-ventricular assist configuration, in a right-ventricular assistconfiguration or in a bi-ventricular assist configuration. For instance,if the left-ventricular assist configuration is adopted, the rotary pumpis connected between the left ventricle of the patient's heart and theaorta. Generally, a rotary pump includes a housing having an inlet andan outlet, an impeller positioned within the housing and impeller bladesextending from the impeller. The blood enters the inlet of the housingand is pumped by the rotating impeller through the housing to the outletand into the patient's circulatory system.

Blood pumps are a unique class of devices. This is so, inter alia,because artificially pumping blood presents many issues that are notpresent when pumping fluids in pumps that need not be biocompatible.When pumping blood, it is imperative to prevent damage to the bloodcells because this can lead to the activation of platelets, coagulationand potentially fatal thrombosis. For instance, because coagulation canresult from increased temperatures, the temperature of the blood must becarefully controlled. Moreover, blood cells may coagulate or albumin ofthe blood denature if the blood temperature reaches forty-two degreescentigrade (42° C.). Even at lower temperatures, some adverse effectsmay occur. If a blood pump is relatively inefficient, the pump canimpart excessive energy to the blood, which usually takes the form ofheat. Therefore, it is imperative that blood pumps be efficient to avoidtransferring heat to the blood. Per force, effective heat management isvery important. Further, sudden flow retardations may cause excessiveshear stresses.

Moreover, numerous studies have proven that exposing blood to highstresses, such as shear stresses, results in immediate or delayeddestruction of blood cells. As a result of the rotation of an impeller,regions of turbulence, jet formation, cavitation and rapid accelerationmay be created in blood pumping operations, causing the blood cellsflowing through the pump to break down and rupture. Further, edges orprotruding surfaces within a blood pump can cause shear stresses and thebreakdown of blood cells. Also, the geometric configuration of a pumpmay cause localized regions of retarded flow or stagnation. Flowstagnation can cause blood elements to deposit on the pump structure,coagulate and possibly result in thrombosis.

Many attempts have been made to meet the design constraints for usingblood pumps as ventricular assist devices. One type of conventionalrotary pump utilizes mechanical bearings that necessitate a lubricantflush or purge with an external lubricant reservoir for lubricating thebearing and minimizing heat generation. Examples of this type of rotarypump are illustrated in U.S. Pat. Nos. 4,944,722 and 4,846,152 issued toCarriker et al. and Wampler et al., respectively. There are manydisadvantages of this type of rotary pump. The percutaneous supply ofthe lubricant purge fluid degrades the patient's quality of life andprovides the potential for adverse reaction and infection. Seals for theexternal lubricant are notoriously susceptible to wear and to fluidattack, which may result in leakage. This may cause the pump to seize.Also, an additional pump is needed for delivery of the lubricant to thebearing. Yet another disadvantage of this type of rotary pump is thatthe bearings need to be replaced over time because of wear due to thebearings directly contacting other pump structures.

In order to eliminate the need for an external purge of lubricant,rotary pumps having a magnetically suspended impeller have been created.By utilizing a magnetically suspended impeller, direct contact betweenthe bearing and other pump structures, as well as external lubricantpurges are eliminated. Examples of this type of rotary pump aredisclosed in U.S. Pat. Nos. 5,326,344 and 4,688,998 issued to Bramm etal. and Olsen et al. respectively. These types of rotary pumps generallyinclude an impeller positioned within a housing, wherein the impeller issupported and stabilized within the housing by a combination ofpermanent magnets positioned in the impeller and the housing andelectromagnets positioned within the housing. The impeller is rotated bya ferromagnetic stator ring mounted within the housing and electromagnetcoils wound around two diametrically opposed projections. Theferromagnetic impeller and the electromagnetic coils are symmetricallypositioned with respect to the axis of the rotary pump and thus, imposean axially symmetric force on the fluid passing through a single annulargap formed between the housing and the impeller.

A disadvantage of these types of rotary pumps is that there is only oneannular gap for the blood to pass through, which serves competingpurposes with respect to fluid flow and the magnetic suspension androtation of the impeller. Regarding fluid flow, the gap is desired to belarge for efficient pumping whereas, for efficient suspension androtation of the impeller, the gap is desired to be small. In this typeof rotary pump, the fluid gap must be relatively small, so as to providethe proper magnetic suspension. This does not allow for efficientpumping of blood because the gap must be made relatively small.

Blood pumps have been designed with hydrodynamic bearings, as opposed tomagnetic bearings. Due to the differential pressure across these typesof bearings any flushing of these types of bearings is generallyminimal. Thus, these types of pumps generally have a relatively stagnantregion of blood within the bearing. Therefore, a drawback of these typesof pumps is that the blood is relatively stagnant in the regions aroundthe bearings, which can lead to the deposition of blood elements,coagulation and potentially thrombosis.

Another concern with ensuring the biocompatibility of blood pumps is tominimize the size of the blood pumps. By minimizing the size of bloodpumps, the amount of foreign surface area that the blood must contactdecreases. This decreases the likelihood that the blood will becomecontaminated or the blood cells will be damaged. There is a competingconcern with minimizing the size of blood pumps. As the size of bloodpumps decreases, the flow paths become narrower, the required rotationalspeed becomes higher and the likelihood of increased shear stressesincreases. Therefore, it is important in designing relatively smallblood pumps to prevent excessive shear stresses.

The blood pumps of the present invention provide for improvements inpumping blood. These features are related, inter alia, to the magneticsuspension of the rotor and enhancing the biocompatibility andreliability of the pumps through certain geometric features of the pumpswhile simultaneously minimizing the size of the pumps.

SUMMARY OF THE INVENTION

The blood pumps of this invention have a housing, a stator or stationarymember and a rotor magnetically suspended between the stator and thehousing. A primary flow path may be defined between the housing and therotor and a secondary flow path may be defined between the stator andthe rotor. The primary flow path provides the flow path for thesubstantial majority of blood flowing through the pump. Defined withinthe pump may be a radial magnetic bearing that suspends the rotorradially within the pump. Preferably, the radial magnetic bearingincludes a stack of magnets disposed in the rotor and a stack of magnetsdisposed within the stator and aligned with those in the rotor. Thesetwo stacks of magnets interface across the secondary flow path tosuspend the rotor radially from the stator. By providing a secondaryflow path across which the radial bearing operates, the primary flowpath can be large enough to provide an adequate flow rate or volume ofblood pumped.

The pumps may also have a thrust bearing for controlling the axialposition of the rotor. In a preferred embodiment, the thrust bearingincludes the radial bearing, thrust coils disposed within the housing,pole pieces, disposed within the rotor, a sensor and a controller. Theradial bearing also produces a force in the axial direction. The thrustcoils which are preferably disposed in the housing, cooperate with thepole pieces, which are preferably disposed in the rotor, to produce acounteracting force in the axial direction. The blood flowing throughthe pump also imparts an axial force on the rotor. In order to maintainthe rotor's axial position, the pumps preferably have the controller andthe sensor referred to above. The sensor preferably includes a sensingcoil disposed within the stator that communicates with the rotor todetermine the axial position of the rotor. The controller is inelectrical communication with the sensor and the thrust coils. Based onthe position sensed by the sensing coils, the controller adjusts theelectrical current through the thrust coils. This adjusts the axialforce exerted on the rotor, so that the rotor can be positioned to itspreferred axial location within the pump. In a preferred embodiment thecontroller is a Virtually Zero Power controller.

The motor stator for driving the rotor is preferably disposed within thehousing and communicates with a rotor magnet across the primary flowpath to rotate the rotor. By placing the motor stator within thehousing, as opposed to the stator or stationary member around which therotor rotates, the heat generated by the motor can be more easilydissipated away from the blood. This enhances the biocompatibility ofthe pumps. Further, by placing the motor stator within the housing,larger wire can be used due to the increased volume in the housingrelative to the motor stator. This is significant because using largerwire reduces the ohmic heating of the motor stator.

As alluded to above, the rotor is magnetically suspended by theinteraction of magnets across the secondary flow path. The secondaryflow path is of a size that balances two competing considerations. Thesecondary flow path must be large enough to provide adequate flushingthroughout the secondary flow and thereby prevent stagnation and thecollection of blood cells along localized regions of the secondary flowpath. Stagnation and the collection of blood cells can lead tothrombosis and eventually embolization. The secondary flow path mustalso be small enough, so that the radial magnetic bearing operateseffectively in order to minimize the size of the pump and the foreignsurface area in contact with the blood. Thus, the secondary flow path isoptimally sized so as to balance these competing considerations.

In a preferred embodiment, the flow through the secondary flow path canbe retrograde, opposing the direction of flow through the primary flowpath. Increased flushing of the secondary flow path can be achieved withretrograde flow. It has been found that if flow is in the same directionas the primary flow path, the flow rate is insufficient to provide thedesired amount of flushing without further increasing the size of thesecondary flow path and the pump.

Preferably, the stator, the rotor and the housing are all shaped so asto create streamlined or relatively smooth flow paths for the blood andto prevent relatively sharp surfaces or edges from contacting the blood.As described above, such surfaces are undesirable because they increaseshear stresses on the blood and increase the likelihood that blood cellswill collect at such a surface and coagulate.

Other features of the invention are provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings show the present preferred embodiments of theInventions in which:

FIG. 1 is a cross-sectional view of a present preferred embodiment of arotary fluid pump having a magnetically suspended impeller.

FIG. 2 is a perspective view of the impeller of the rotary fluid pumpshown in FIG. 1.

FIG. 3 is a cross-sectional view of the motor stator and motor rotor ofthe rotary fluid pump shown in FIG. 1 taken along line III—III.

FIG. 4 is a cross-sectional view of the stator member and impeller ofthe rotary fluid pump shown in FIG. 1 taken along line IV—IV.

FIG. 5 is a schematic diagram of the magnetic bearing control used inthe rotary fluid pump shown in FIG. 1.

FIG. 6 is a schematic view of a passive radial bearing which is apermanent magnet bearing stator member.

FIG. 7 is a schematic view of the passive radial bearing of FIG. 6having an axial offset.

FIG. 8 is a cross-sectional view of a passive radial bearing where thepole pieces are notched to provide pole saliency.

FIG. 9 is a cross-sectional view of another salient type passive radialbearing having a thrust bias which is equivalent to a passive radialbearing with axial offset.

FIG. 10a is a cross-sectional view of an active radial bearing withlarge fluid flow regions.

FIG. 10b is a cross-sectional view of the active radial bearing of FIG.10a taken along line X—X.

FIG. 11 is another view of a passive thrust bearing.

FIG. 12 is a cross-sectional view of a passive thrust half bearingwherein the two components are contoured to one another.

FIG. 13 is another passive thrust bearing where pole pieces are notchedprovide pole saliency.

FIG. 14 is another active thrust bearing.

FIG. 15 is an active thrust half bearing.

FIG. 16 is another active thrust half bearing.

FIG. 17 is a first embodiment of an active thrust bearing.

FIG. 17A is a second embodiment of an active thrust bearing.

FIG. 17B is a third embodiment of an active thrust bearing.

FIG. 17C is a fourth embodiment of an active thrust bearing.

FIG. 18 is a hybrid of an active radial bearing and a passive thrustbearing.

FIG. 19 is a hybrid of an active thrust half bearing and a passiveradial bearing.

FIG. 20 is a hybrid of a stator of an induction motor and an activethrust half bearing.

FIG. 21 is a cross-section of the stator shown in FIG. 20 taken alongthe line XXI—XXI.

FIG. 22 is an armature of a hybrid of an induction motor and an activehalf thrust bearing.

FIG. 23 is a cross-section of the armature shown in FIG. 22 taken alongline XXIII—XXIII.

FIG. 24 is a cross-sectional view of a two-pole motor having fourimpeller blades which is an alternative motor for the rotary pump shownin FIG. 1.

FIG. 25 is a cross-sectional view of a variable reluctance motorhybridized with impeller blades.

FIG. 26 is a cross-sectional view of an induction motor hybridized withimpeller blades.

FIG. 27 is a cross-sectional view of another variable reluctance motor.

FIG. 28 is a cross-sectional view of another induction motor.

FIG. 29 is a flow chart illustrating a computational fluid dynamicsmethod used to design the geometric configuration of the embodiments ofthe present preferred invention.

FIG. 30 is a partial cutaway cross-sectional view an alternateembodiment of the rotary fluid pump of the present prefigured inventionhaving an inducer blade positioned on the impeller and an inflow cannulaand an outflow cannula positioned at the inlet and outlet of thehousing, respectively.

FIG. 31 is a cross-sectional view of an alternate embodiment of therotary pump of the present preferred invention.

FIG. 32 is a cross-sectional view of the brushless DC motor of therotary fluid pump shown in FIG. 31 taken along line XXXII—XXXII.

FIG. 33 is a cross-sectional view of the axial conical magnetic bearingof the rotary fluid pump shown in FIG. 31 taken along lineXXXIII—XXXIII.

FIG. 34 is another alternate embodiment of the rotary fluid pump of thepresent preferred invention.

FIG. 35 is the cross-sectional view of the rotary fluid pump of FIG. 34taken along line XXXV—XXXV.

FIG. 36 is a cross-sectional view of another embodiment of the rotarypump of the present invention wherein the rotary pump takes the form ofa centrifugal pump.

FIG. 37 is a cross-sectional view of the centrifugal pump of FIG. 36taken along the line XXXVII—XXXVII.

FIG. 38 is an alternative preferred embodiment of a blood pump of thisinvention;

FIG. 39 is an end view of the outlet of the preferred embodiment of FIG.38.

FIG. 40 is an end view of the inlet of the preferred embodiment of FIG.39.

FIG. 41 is a cross-section taken along line 41—41 of FIG. 39.

FIG. 42 is a cross section taken along line 42—42 of FIG. 41.

FIG. 43 is a side view of a preferred embodiment of the rotor and thestator of the preferred embodiment of FIG. 39.

FIG. 44A is an isometric view of a preferred embodiment of a second endof the stator of FIG. 43.

FIG. 44B is an end view along line 44B—44B of FIG. 43.

FIG. 45 is a diagrammatical view illustrating the preferred flow pathsof the preferred embodiment of FIG. 38.

FIG. 46 is a diagrammatical view of a preferred embodiment of some ofthe bearings of the preferred embodiment of FIG. 39.

FIGS. 1 through 5 illustrate a present preferred embodiment of theinvention substantially comprising an axial rotary pump having a housing12, an impeller 14 with impeller blades 16, a stator member 18, meansfor levitating the impeller 14 within the housing 12 at a centeredposition and means for rotating the impeller 14. The housing ispreferably cylindrical and has an internal surface 20, an externalsurface 22 concentrically spaced from the internal surface 20, an inlet24 and an outlet 26. The internal surface defines an internal region 28in which the impeller 14 is positioned. The impeller 14 (FIG. 2) has asubstantially axially symmetric elongated body 30, a conical-shaped nose32 and a conical-shaped tail 34, as best shown in FIG. 2. Magnetictargets 36 and 38 are positioned over the impeller nose 32 and theimpeller tail 34, respectively. The impeller blades 16 are substantiallyhelical soft magnetic material and are attached to permanent magnets 13on the body of the impeller 14, as best shown in FIG. 3.

The stator member 18 has an upstream set of stationary blades 40, adownstream set of stationary blades 42, a motor stator 44 and an anglesensor 46, as shown in FIG. 1. The upstream set of stationary blades 40and the downstream set of stationary blades 42 are attached to thehousing 12 and converge toward the longitudinal axis 48 of the housing12, wherein the free ends of the upstream set of stationary blades 40and the free ends of the downstream set of stationary blades 42 definean upstream passageway 50 and a downstream passageway 52, respectively.The impeller nose 32 and the impeller tail 34 extend within the upstreampassageway 50 and downstream passageway 52 respectively, such that gaps54 and 56 are formed between the free ends of the upstream anddownstream sets of the stationary blades 40 and 42 and the impeller nose32 and the impeller tail 34, respectively. As can be best seen in FIG.4, the downstream set of stationary blades 42 further defines fluid flowregions within the internal region 28, as seen in FIG. 1, of the housing12. Although not shown, similar fluid flow regions are defined by theupstream set of stationary blades 40. Although FIG. 4 is a cross-sectiontaken through the downstream set of stationary blades 42, it will beappreciated that a similar cross-section taken through the upstream setof stationary blades 40 would be substantially identical. The upstreamand the downstream sets of stationary blades 40 and 42 are preferablymade from soft magnetic material; however, they can be made frompermanent magnets located in series. Although each set of the upstreamand downstream sets of stationary blades 40 and 42, are shown ascomprising four stationary blades, other combination of blades can beused.

The means for rotating the impeller is a brushless DC motor having amotor stator 44, an angle sensor 46, an impeller elongated body 30having permanent magnets 13, flux focusing structures 15 made from asoft magnetic material, and impeller blades 16 which serve as the motorpoles and are made from a soft magnetic material coated with abio-compatible material. The motor stator 44 and the angle sensor 46 arepositioned within the housing 12 between the internal surface 20 and theexternal surface 22. Motor stator coils 66, as shown in FIG. 3, arewound on the motor stator 44. The current through the motor stator coilcan be controlled to affect the desired speed of the impeller with aconventional means. Although this is the preferred means for rotatingthe impeller, a variety of other rotational means can be used in theinvention. Alternatively, the brushless D.C. motor can take the form ofa two pole motor.

The means for levitating (FIG. 4) the impeller 14 are conical bearingswhich includes independently controlled coils 60 wound around thebackiron segments 62, which are made from a soft magnetic material,segmented and radially magnetized permanent magnets 64, and fourstationary blades 42, which act as pole pieces. The coils 60 arecontrolled to center the impeller 14 between the stationary blades 42.This design is particularly suited for use where fluid flow is requiredthrough the four fluid flow regions 58. The levitation means depicts anactive radial bearing.

This conical bearing provides radial stiffness and axial stiffness whenit is controlled with a feedback system and amplifier. Electromagneticcoils 60 wound around the backiron segments 62 direct the magnetic fluxfrom the electromagnetic coils 60 such that the impeller tail 34 issuspended and substantially centered within the downstream passageway52. Further, permanent magnets 64 are provided within the backironsegments 62 in order to provide a permanent bias thus, reducing therequired steady state current. By winding electromagnetic coils 60around the backiron segments rather than around the downstream set ofstationary blades 42, the fluid flow regions 58 remain large enough forblood to pass therethrough without forming regions of stagnation orturbulent flow.

Position sensors 65 are attached to the inlet 24 and the outlet 24 ofthe housing 12 and adjacent to the impeller nose 32 and the impellertail 34. Any position sensor can be used including a Hall-effect,eddy-current, or infrared optical sensors. The impeller 14 position caneven be sensed from changes in inductances of the coils 60. Magneticbearings controlled with such a sensing scheme are referred to assensorless bearings when used in conjunction with bearings as describedin “Analysis of Self-Sensing Active Magnetic Bearings Working OnInductance Measurement Principle,” D. Vischer et al., SecondInternational Conference on Magnetic Bearings, Tokyo, pp. 301-309, July1990.

In order to magnetically levitate the impeller 14 a feedback controlleris used as diagramed in FIG. 5. Position errors are measured with 8position sensors 65 and transformed into error signals x_(i), z_(o),x_(o), z_(i) and y, while x_(i) and z_(i) measurements correspond to thex and z impeller displacement of the impeller measured at the inlet 24,and x_(o) and z_(o) are measured at the outlet 26. The errortransformation is accomplished with the sensor decoupler 70 shown inFIG. 5 which is simply a matrix multiplication accounting for theposition and orientation of the sensors 65. The five principledisplacement errors are filtered independently with the five channelcontroller 72, which outputs five desired restoring forces to be appliedto the impeller 14. The bearing decoupler 74 transforms these commandsvia a matrix multiplication into an appropriate coil current pattern tobe applied to the coils 60. The current commands are input to anamplifier 76 which drives the coils 60. The principle of decoupling iswell-known, as are various kinds of controls used in the five channelcontroller. Some examples of control algorithms areproportional-integral-derivative and zero-power control algorithms. Themagnetic bearing sensors and impeller dynamics 77 model how the bearingfluxes react to the coil currents and how the impeller responds to themagnetic forces created by the bearing fluxes.

During operation of the rotary pump 10, the blood enters the inlet 24 ofthe housing 12 in the direction of arrow A. The blood passes over theimpeller nose 32 through the gap 54 and the fluid regions 58 shown inFIG. 4. The upstream set of stationary blades 40 serve to straighten theincoming blood flow. The impeller 14 is rotated by the rotating meansand the impeller blades 16 accelerate and impart energy to the bloodsuch that the blood moves through the housing 12 toward the outlet 26.The downstream set of stationary blades 42 function to recover velocityenergy in the form of pressure energy from the blood flow exiting theimpeller blades 16. Before exiting the housing 12, the blood passesthrough the gap 56 and the fluid flow regions 58 formed by thedownstream set of stationary blades 42. The gaps 54 and 56 are sized andproportioned such that they are large enough to prevent regions ofstagnation and excessive shear from forming while being small enough toprovide efficient magnetic suspension of the impeller 14. Furthermore,the axially symmetric configuration of the impeller elongated body 30provides for blood to flow through the housing 12 without creatingregions of stagnation or excessive shear.

As noted above, the impeller nose 32 and the impeller tail 34 aremagnetically suspended and centered within the housing 12 by themagnetic flux created by the electromagnetic coils 60 and directedthrough the upstream and downstream sets of stationary blades 40 and 42.The gaps 54 and 56 are small enough to allow for the magnetic flux to bedirected across the gaps without a substantial increase in the magneticcircuit reluctance. If during pumping of the blood, the impeller 14moves from its centered position within the housing 12, position sensors65 will detect this movement and the means for levitating the impeller14 will apply a net force and moment to the impeller 14 to repositionthe impeller 14 to its centered position within the housing 12. Forexample, a net force in the y direction is accomplished by increasingthe flux in the outlet gap 56 and decreasing the flux in the inlet gaps54 with appropriate corresponding coil currents. The calculation of thecurrents is accomplished with the sensor decoupler of the five channelcontroller 72, and the bearing decoupler 74 working in combination.Alternatively, the sensing of the movement of the impeller 14 can beaccomplished by estimating the coil inductances from the coil voltagesand current and then calculating the gap from the coil inductances.

The variation of magnetic components which include both electric motorsand magnetic bearings is extensive and well-documented. Below aredescribed some typical magnetic components and how some of thesemagnetic components can be used in embodiments of the present preferredinvention.

Passive Radial Bearing (PRB): FIG. 6 shows a common design of a passiveradial bearing (PRB) which is a permanent magnet bearing. It consists ofalternatively magnetized annular permanent magnets 100 a, 100 b, 100 c,100 d, 102 a, 102 b, 102 c and 102 d comprising two annular magnet rings110 and 112, respectively, of the passive radial bearing. Either annularring 112 or 110 can serve as either the impeller or the stator of arotary pump. The number of permanent magnets in the embodiment of therings 110, 112 shown is the same, but not necessarily four. Othernumbers of magnets may be employed.

The annular magnet rings 110 and 112 are magnetized to provide radialstiffness. However, it is a property of this type of bearing that theaxial stiffness is negative with a magnitude equal to twice the radialstiffness. Although this negative stiffness cannot be used alone foraxial positioning, it can be used to provide axial bias forces as shownin FIG. 7. By axially shifting the annular magnet rings 110 and 112relative to each other net steady state forces 120 and 122 can beapplied in the axial direction as shown by the arrows. This is due tothe fact that magnet 102 a is applying a force on magnet 100 a in thedirection 120 and magnet 102 b is applying a force on magnet 100 a inthe direction 120. Similar interaction occur amongst the other magnets.Passive radial bearings are further described in “Stacked Structures ofPassive Magnetic Bearings”, J. P. Yonnet et al., Journal of AppliedPhysics, vol, 70, no-10, pp. 6633-6635, which is hereby incorporated byreference.

Another kind of PRB is shown in FIG. 8. This bearing has a stator 130 awhich includes stator magnets 130 and 134 and soft magnetic stator polepieces 132, 136, 138, 140. The bearing impeller 148 is a soft magneticmaterial with teeth 144. Permanent magnets 130 and 134 are magnetizedaxially, so that a magnetic flux passes through pole pieces 132, 136,138, and 140 and through the bearing impeller 148 in a closed loop asshown by arrow 149. The impeller teeth 144 and the stator teeth 142 tendto align to minimize the reluctance of the magnetic circuit whichresults in the radial position of this bearing. This passive radialbearing is unstable in the axial direction as is the bearing of FIG. 6.The recesses 146 defined by teeth 142 may be filled with nonmagneticmaterial to eliminate blood stagnation zones. Although in FIG. 8, thestructure designated by reference number 148 rotates and serves as theimpeller, and the structure designated by reference number 130 a servesas the stator, it will be appreciated that the structure designated byreference number 148 could be fixed, so that it serves as the stator.Likewise, the structure designated by reference number 130 a could befree to rotate and have the impeller blades, so that it serves as theimpeller.

FIG. 9 illustrates a passive radial half bearing (PRB2). This bearing issimilar to that of FIG. 8 in that it provides radial position to theimpeller 148, but unlike the PRB of FIG. 8 it provides a bias force onthe impeller 148 in the direction 150.

Active Radial Bearing (ARB): FIGS. 10a and 10 b depict an active radialbearing (ARB). The bearing stator consists of soft magnetic materialbackiron segments 151. segmented and radially magnetized permanentmagnets 153, independently controlled coils 155 and four pole pieces157. The rotor 159 is a soft magnetic material. The permanent magnetshave magnetizations such that they provide a bias flux in the four gaps161 between the rotor and the stator. The direction of this bias isshown with the four arrows 163. The stator coils are controlled tocenter the rotor around the stator. This design is particularly suitedfor use where fluid flow is required through the four bearing passages165.

This bearing provides radial stiffness and essentially little axialstiffness when it is controlled with a feedback system and amplifier.

Passive Thrust Bearing (PTB) and Passive Thrust Half Bearing (PTB2):FIG. 11 illustrates a passive thrust bearing. The bearing rotor 152supports two magnet stacks 154 and 156 which repel magnetstacks 158 and160 on the stator 162. The net effect of the magnetic interaction isthat the bearing has a positive axial stiffness and negative radialstiffness.

A similar bearing is shown in FIG. 12 which only applies thrust to therotor 164 a in the direction 164. Such a bearing is called a passivethrust half bearing (PTB2). All bearing gaps can be contoured to providefor blood flow without stagnant and separated flow.

FIG. 13 shows a thrust bearing which uses the same principles as theradial bearing of FIG. 8 but is distinguished from FIG. 8 in that theaxial gaps of FIG. 8 are reoriented as radial gaps in FIG. 13.

Active Thrust Bearing (ATB) and Active Thrust Half Bearing (ATB2): FIG.14 depicts an active thrust bearing. The stator consists of pole pieces166 and 168 and coils 170 and 172 which are driven independently.Applying a current to coil 170 causes the stator pole piece 166 to lineup with impeller teeth 174 by applying a force on the impeller 175 inthe direction 176. Similarly, energizing coil 172 applies a force in theimpeller 175 in the direction 178. By sensing that the axial position ofthe impeller 175. feedback controls can position the impeller 175axially. These bearings exhibit moderate negative radial stiffness, andtherefore require active control. FIG. 15 shows active thrust halfbearing (ATB2) which only applies force in the direction 180 to theimpeller 182.

FIG. 16 illustrates an alternate active thrust half bearing. The statorconsists of soft iron or ferromagnetic pieces 184 and 186 driven by apermanent biasing magnet 188 in the direction 190. The bias flux ismodulated by the control coil 192, so that the force applied to the softmagnetic target 194 is controlled. This is an ATB2 because force isapplied to the impeller only in the direction 198. FIG. 17 shows an ATBcomprised of two ATB2's which are based on the same principles as FIG.16.

FIGS. 17A-17C illustrate alternative types of active thrust bearingsthat may be used with the pump of this invention. Illustrated in theseFigures are active thrust bearings that include Lorentz force actuators.As shown in FIG. 17A, a Lorentz force actuator includes coils 199 a,preferably made of copper through which an electrical current flows. Themagnetic field generated by these coils interacts with magnets 199 d andpole pieces 199 c disposed in the rotor to position the rotor axially.The currents in the two coils 199 a are preferably equal and of oppositedirections.

FIG. 17B illustrates another type of Lorentz force actuator in which thecopper coils 199 a interact with a single magnet 199 b to control theaxial position of the rotor. FIG. 17C depicts a third type of Lorentzforce actuator that includes an outer iron member 199 d, copper coils199 a and a single magnet 199 b.

Hybrid Components: It is often possible to physically integrate thefunction of two magnetic components. For example, FIG. 18 shows the ARBof FIGS. 10a and 10 b with teeth 200 and 202 added to the rotor 204 andstator 206, respectively. The magnetic field across the gap 208 of thebearing cause the teeth 200 and 202 to align passively without feedbackcontrol hence this is a hybrid of a PTB and an ARB which is denoted as“PTB=ARB.”

A similar hybrid is shown in FIG. 19. Coil 210 is added to a PPB whichis half the PRB of FIG. 9. This coil actively controls thrust in onedirection along the rotor axis. Because the function of an ATB2 is addedto a PRB, the resulting hybrid is denoted as “ATB2=PRB.”

The inlet-conical bearing in FIG. 1 is a hybrid of an active radialbearing and a thrust half-bearing because the pole face angles areintermediate between a thrust bearing and a radial bearing. The poles ofthe conical bearing also serve as pump stator blades.

Hybridization of fluid and magnetic components is also possible. Pumpblades, both impeller and stator blades, can be used as magnetic fluxpaths. The stator blades in FIG. 1 act as magnetic poles for the conicalmagnetic bearings. Furthermore, the impeller blades are flux paths forthe brushless DC motor in FIG. 1. It is also possible for stator bladesto serve as supports for passive magnetic bearing stators, and forimpeller blades to support magnetic structures.

FIGS. 20 through 23 illustrate a pancake induction motor which can becontrolled for thrust as well. FIGS. 20 and 21 show a stator with statorpoles 212 and stator coils 214 for a pancake induction motor. FIGS. 22and 23 show an armature 222 with magnetic iron members 216 and slotconductors 218. Annular regions 220 and 223 are also conductors. Bycontrolling the six stator coil currents it is possible tosimultaneously vary the motor torque and thrust forces across thepancake motor. This can be done by varying the rotational frequency ofthe stator field and the amplitude of the stator field independently.Similar hybridization of a variable reluctance type motor is describedin U.S. Pat. No. 4,683,391.

An alternative embodiment of the motor to be used as rotation means isthe two pole type brushless DC motor 224 a shown in FIG. 24. The rotor224 b is shown along with the stator. The stator coils are not shown inFIG. 24, but are similar to those of FIG. 3.

Alternative Means of Rotation: An alternative motor configuration forFIG. 1 is shown in FIG. 25. This is a variable reluctance type motorwhere the rotor poles and the impeller blades are hybridized. The rotor224 is made from a soft magnetic material as are the blades 226. Thecommutation for this motor is different from that for the DC brushlessmotor, but well known to those skilled in the art of motor control.

FIG. 26 is yet another possible motor configuration to be used in therotary pump shown in FIG. 1. It is an induction motor whose impellerslot structure is hybridized with the impeller blades 228. By applying arotating magnetic field to the impeller via the stator coils 230,currents are induced in the slot conductors 232 which have currentreturn paths connecting adjacent slots conductors, that are not shown,but exist on the axial end caps of the impeller.

FIG. 27 depicts a variable reluctance motor cross section to be used inthe rotary pump of the present preferred invention. The impeller of thismotor 236 is made from soft magnetic material (e.g. approximately 3%silicon-iron).

FIG. 28 is an induction motor. The cross-section of the motor depictsslot conductors 238 and a soft magnetic material impeller 240. Slotconductor end-turn current paths are not shown.

The following acronyms can be utilized to describe variousconfigurations for the rotation means and the levitation means of thepresent preferred invention.

Pump Type Descriptors

FH fixed hub

RH rotating hub

AO axial outlet

RO Radial outlet

Sp fixed-hub support

sb stator blade

ib impeller blade

Magnetic Components

ARB active radial bearing

ATB active thrust bearing

ATB2 active thrust half-bearing

PRB passive radial bearing

PRB2 passive thrust half bearing

VRM variable reluctance motor

DCBM direct current brushless motor

IM induction motor

Other Notations

x is used to indicate a magnetic component X, where the magnetic gap ispositioned adjacent the housing

x is used to indicate a magnetic component X, where the magnetic gap isadjacent the hub.

— a line segment indicates that two components are consecutive along theblood flow path.

= an equal sign indicates that two components are functionallyintegrated or “hybridized.”

 is used to indicate that the component X is hybridized with impellerblades.

 is used to indicate that the component X is hybridized with statorblades.

 indicates components X and Y are aligned for structural support.

 (RH, AO) parenthetical acronyms denote the design type. In this case“rotating hub with axial outlet.”

With these notations we can represent the pump in FIG. 1 by thefollowing formula.

Each formula consists of a “header” defining the hub type (RH or FH) andthe outlet type (AO or RO), followed by an “upper sentence” describingthe order and kinds of magnetic components, gap locations either at thehousing or hub and whether or not they are hybridized. Positions of hubsupports are also noted in the upper sentence. There is also a “lowersentence” describing the order of fluid components vertical alignmentbetween the upper sentence and the lower sentence does not imply anyphysical alignment unless a “′” is used to indicate alignment or a “∥”is used to indicate that components in the two sentences are hybridized.

Formula (1) describes a design which is a rotary hub type (RH) withaxial outlet (AO). The components from inlet to outlet along the bloodflow path are a stator blade hybridized with an active radial halfbearing which forms a conical bearing and the hybridized bearing has itsmagnetic gap toward the inside diameter of the primary fluid flow path.Reading formula 1 further, a brushless DC motor is hybridized with theimpeller blades and has its magnetic gap toward the outside diameter ofthe fluid flow path. Reading formula 1 further, an active radial bearingis hybridized with an active thrust half bearing which is furtherhybridized with a set of stator blades.

Using this language many of the embodiments of the rotary pump of thepresent preferred invention are enumerated. By applying physicalconstraints, designs are eliminated which are not practical.

A formula header is any one of (FH, AO), (FH, RO), (RH, AO), or (RH,RO). A formula upper sentence is any sequence of magnetic componentsacronyms and/or support acronyms separated by “—” or “=”. The magneticcomponent acronyms are either underlined or not. The lower sentence isany sequence of impeller blade acronyms or stator blade acronyms. Eachacronym in the lower sentence may be aligned with one acronym in uppersentence provided that order is preserved; that is, if an acronymidentifying a magnetic component (A) and an acronym denoting a fluidcomponent (B) are aligned with a “|” or hybridized with “∥”, and anacronym denoting a magnetic component (C) and an acronym denoting afluid component (D) are aligned, and if C follows A in the uppersentence we must have D following B in the lower sentence we call thisthe “order preserving” property.

Certain formulas can be eliminated because they violate the followingsimple structural requirements. All formulas with the header (RH, RO)are eliminated due to the existence of a stagnation zone in thisconfiguration. If the bearing is RH type then Sp may not appear in theupper sentence because supports are only needed for the fixed hub (FH)type pump. No two magnetic components may be separated by a fixed hubsupport (Sp). If this were to happen the impeller would be divided intotwo separate pieces. The lower sentence must include at least oneimpeller blade (ib). if the header contains a fixed hub (FH), then theupper sentence must contain at least one support (Sp). The uppersentence must include one motor; however, we may have additional motorsto add reliability. The magnetic components must satisfy force/momentbalance for x, y, z, pitch (⊖) and yaw (φ) motions of the impeller. Thatis, any bias force associated with PRB offsets or ATB2's must balance.

Collectively the magnetic bearing components, both active and passivemust provide positive stiffness (i.e., positive restoring forces tolevitation) in the x, y, z, pitch and yaw directions because the motorcontrols the roll direction. This is characterized mathematically with apositive definite symmetric stiffness matrix, K, relating the fivedisplacements, x, y, z, pitch and yaw to the corresponding restoringforces and moments. Consider a coordinate frame at the center of mass ofthe rotor with its axes aligned as shown in FIG. 1. Pitch is rotationabout the x-axis; yaw is rotation about the z axis; and roll is rotationabout the y-axis and is controlled by the motor. Let (Δx, Δy, Δz, Δθ,Δφ)^(T) be the vector of x, y, z, pitch and yaw displacements of theimpeller relative to the desired levitated position, where superscript“T” denotes transpose. Further, let the vector of corresponding forcesand moments measured in the given frame be (f_(x), f_(y), f_(z), m_(θ),m_(φ))^(T) and let K be the “support stiffness matrix” of the rotorsatisfying (f_(x), f_(y), f_(z), m_(θ), m_(φ))^(T)=−K(Δx, Δy, Δz, Δθ,Δφ)^(T). By using appropriate feedback control of active magneticbearings, the axial position of the rotor can be maintained. This can beachieved by using a particular candidate magnetic bearing configurationthat has a positive definite symmetric support stiffness matrix.(positive definite means that for all vectors a variable v≠O, v^(T)Kv>O). With feedback control this stiffness property can be achievedonly over a certain frequency band.

If such a support stiffness matrix is achievable for a particular setand placement of magnetic bearings, we say that the magnetic bearingsare “compatible.” This definition of compatibility allows us toenumerate a large number of good designs via computer verification ofthe positive definiteness of the support stiffness matrix.

Using the enumeration methodology outlined above we can deriveadditional embodiments of the present preferred invention. Alternativeembodiments are:

Additional good embodiments have the following formulas.

Having isolated thrust bearing:

Having outboard motor:

The geometric configurations of the impeller and stator member arecrucial to the hydrodynamic performance and the biocompatibility of therotary pump. Specifically, the flow path must be designed to avoidregions of high fluid stress which may damage cells or activate theclotting process. Further, regions of blood stagnation that may resultin depositions of blood elements on the blood pump structure should alsobe avoided because they may cause embolism and possibly stroke. Acomputational fluid dynamics method is employed to design the geometricconfigurations of the impeller, stator member, and the housing whichtakes into consideration the specific characteristics of blood flow suchas the tendency of blood to clot when regions of stagnation develop, andthe propensity of blood cells to rupture when excessive stress is placedthereon.

In FIG. 29 illustrates a flow chart describing the computational fluiddynamics-based method used to design the geometric configurations of thepresent preferred invention. This method for designing a rotary fluidpump substantially comprises the steps of: (a) selecting an initialgeometric configuration of a part of a rotary fluid pump; (b) convertingthe geometric configuration into parametric form; (c) selecting a fluiddynamic model for blood flow; (d) choosing an objective function to beminimized; (e) determining the flow solution and value of the objectivefunction for the initial geometric configuration; (f) determining thedesign search direction for the initial geometric configuration which isbased on gradients of the objective function with respect to designvariables; (g) selecting a second geometric configuration of the part ofthe fluid pump being designed by changing the geometric designparameters using the search direction information; (h) determining theflow solution and value of objective function for the second geometricconfiguration; (i) comparing the objective function for the firstgeometric configuration with the objective function for the secondgeometric configuration; (j) if the objective function for the secondgeometric configuration is less than the objective function for thefirst geometric configuration, the second geometric configurationbecomes the initial geometric configuration and steps (g) through (j)should be performed until the objective function for the secondgeometric configuration is greater than the objective function for theinitial geometric configuration, and the global design criterial shouldthen be evaluated; (k) if the global design criteria indicates thatfurther design improvement may be possible, the second geometricconfiguration becomes the initial geometric configuration and steps (f)through (k) should be performed until no further design improvement isdeemed possible; alternatively, the initial design configuration istaken to represent the final design configuration. The final geometricconfiguration defines the shape of the part of the rotary pump thatminimizes stagnant and traumatic flow through the pump. This method canbe used to define one or all of the various parts of a rotary pump suchas, the impeller blades, the impeller hub, the stator blades, the statorhub and the housing interior surface. Other aspects of this method aredescribed in Gregory W. Burgreen, et a., CFD-Based Design Optimizationof a Three Dimensional Rotary Blood Pump, AIAA Paper No. 96-4185,1773-1779 (1996), presented at the 6th ALAA/NASA/ISSMO “Symposium onMultidisciplinary Analysis And Optimization” in Bellevue, Wash. which ishereby incorporated by reference.

The model for the blood flow is preferably the incompressibleNavier-Stokes and conservation of mass equations. Use of the formerequations assumes that blood can be treated as a single phase homogenouslinear viscous fluid. In order to solve this equation, a Galerkinfinite-element program was written for this purpose. This program usesquadratic velocity-linear pressure elements within a mixed formulationof the steady equations. These element types are known to be stable andproduce approximations of optimal order. The resulting, non-linearalgebraic system is solved by a Newton continuation method. Analyticalgradients of the objective functions are computed using a directdifferentiation method.

The objective function used in the above-method represents the desireddesign criterion to be minimized. For example, the objective functionsrelating to trauma and platelet activation include, but are not limitedto: shear stress with respect to resident time, viscous energydissipation rates, particle acceleration, negative pressure causingoutgassing or cavitation, and measurements of turbulence intensities.The objective functions defining stagnation and deposition include butare not limited to: vorticity, reverse flow (i.e., boundary layer shearlocally becoming zero), adverse pressure gradient, the standarddeviation of consecutive blade-to-blade axial velocity, and boundarylayer transport. This list is illustrative but is not exhaustive to theobjective functions that can be utilized in the present preferred methodof designing geometric configurations for the rotary pump of the presentpreferred invention.

FIG. 30 illustrates another embodiment of the present preferredinvention which is similar to the rotary pump 10 shown in FIGS. 1through 5 and can be represented by Formula (1) described above. Forpurposes of brevity, only the differences between the two rotary pumpswill be described. The rotary pump 242 substantially comprises a housing244, an impeller 246 positioned within the housing 244, a stator member248; an inflow cannula 250, and an outflow cannula 252, means forlevitating the impeller 246 within the housing 244, and means forrotating the impeller 246. The impeller 246 has a nose 254, a tail 256,and an inducer blade 258 positioned on the nose 254 of the impeller 246.The inducer blade 258 extends around the surface of the impeller nose254. The inducer blade 258, as well as the impeller blades 260preferably are substantially helical in shape. The inducer blade 258functions to augment the blood flow through the housing 244 whiledecreasing cavitation susceptibility. The inflow cannula 250 is attachedto the inlet 264 of the housing 244 and the outflow cannula 252 isattached to the outlet 270 of the housing 244. The inflow cannula 250 isa conduit with a first end 274 and a second end 276. The first end 274is attached to the housing inlet 264 and the second end 276 is capableof being attached to the left ventricle of a heart. The second end 276has a trumpet mouth inlet nozzle 278 with an hourglass exteriorconfiguration. Preferably, the inner diameter of the nozzle 278 tapersfrom twenty millimeters (20 mm) to a final conduit diameter of twelvemillimeters (12 mm). Although both the inflow cannula 250 and theoutflow cannula 252 are shown to be integrated into the housing 244 ofthe rotary pump 242, it is also possible to have cannula employingquick-connecting mechanisms (not shown) in such that the rotary pump canbe quickly detached from the patient.

The stator member 248, the means for rotating the impeller 246 and themeans for levitating the impeller function substantially the same asthose described in FIGS. 1 through 5. It should also be noted that therotary pump 242 does not utilize any position sensors as compared to therotary pump 10, shown in FIGS. 1 through 5, which includes positionsensors 65. A sensorless approach, based on back EMF or coil inductancevariation is used in this embodiment to measure magnetic bearing gapsand impeller angle. Because there are coils in the motor stator and themagnetic bearing stators, voltages induced by impeller motions andself-induced by coil currents can be used to calculate the impellerangle and the magnetic bearing gaps. Examples of methods of sensorlessmagnetic bearings and sensorless motor control are described in: “A NewApproach To Sensorless and Voltage Controlled AMBs Based on NetworkTheory Concepts,” D. Vischer et al., 2nd International Conference onMagnetic Bearings, Tokyo, pp. 301-309, July, 1990; “Sensorless MagneticLevitation Control by Measuring the PWM Carrier Frequency Content,” Y.Okado, et al., Proceedings of the Third International Symposium onMagnetic Bearings, Alexandria, pp. 176-186, July 1992; “Implementationof Sensorless Control of Radial Magnetic Bearings,” R. Gurumoorthy, etal., Proceedings of MAG '95, Alexandria, pp. 239-248, August 1994; andU.S. Pat. No. 5,300,841 issued to M. A. S. Preston et al., forsensorless DC motor control, see the data sheet from Micro LinearCorporation's ML4425 integrated circuit.

FIGS. 31 through 33 illustrate another embodiment of the presentpreferred invention which can be described by Formula 3 noted above. Therotary pump of FIGS. 31 through 33 comprises a housing 280 having aninlet 281 and an outlet 283, a stator 282 with an upstream set ofstationary blades 284 and a downstream set of stationary blades 286, asubstantially cylindrical impeller 288 defining a cavity extendingtherethrough and having impeller blades 290. The stator 282 is asubstantially bell-shaped hub 285. The blood flows primarily throughregion 283. The conical bearing simultaneously centers the outlet end ofthe impeller 288 and supplies a thrust force on the impeller 288 in thedirection of the outlet. The cylindrical permanent magnet bearing 292and 294 supplies radial centering forces for the inlet end of theimpeller 288. An axial force on the impeller 288 in the direction of theinlet 281 is provided by the same magnetic bearings 292 and 294. Thistype of bearing is shown in FIG. 7. The axial forces of the permanentmagnet bearing and the active conical bearing are balanced via theconical bearing control. The permanent magnet bearing of FIG. 7 isstable in the radial direction, but unstable in the axial. By providinga slight offset as shown in FIG. 7, axial forces can be generated in thedirection of the offset.

The means of rotation take the form of a brushless DC motor shown indetail in FIG. 32. The motor has a motor rotor flux return ring 302,stator iron 305 and stator coils 307. Permanent magnets 296 and 298 aremagnetized in the radial direction. One inward and one outward creatinga two pole motor. Region 300 is non-magnetic material suitable forsupporting the permanent magnets. Region 302 is a flux return ring 303for the motor made from soft magnetic material such as 3% silicon-ironor 50% cobalt-iron. Currents in the stator coils 307 are commuted toaffect rotation of the motor. The communication signal is derived fromthe motor impeller angle through the use of back EMF signals on thecoils. This can be accomplished by utilizing an integrated circuit fromMicro Linear Corporation.

FIG. 33 is a section through the conical magnetic bearing depicting thecoils 306, the stator iron 308 made from soft magnetic material, and thebearing rotor 310 made from soft magnetic material. The surface of therotor iron interfacing the secondary blood flow region 312 is coatedwith a biocompatible material. Additionally its surface may be texturedwith rifling or small impeller blades to enhance blood flow through theregion 312.

FIGS. 34 and 35 show another embodiment of the present preferredinvention. The advantages of this arrangement is that there is only oneactive magnetic bearing and brushless DC motor within an enlarged regionof the fixed stator. FIG. 34 illustrates how an ATB2 can be located atthe housing. Because the ATB is disposed in the housing, as opposed tothe stator, there is more room in the stator and the motor can uselarger wire and produce less heat. The rotor comprises a stator 320, andimpeller 322 and a housing 324 with an inlet 326 and an outlet 328. Theinlet 326 allows blood flow into the pump in the direction 330. Thestator 320 is supported by stationary blades 332 at the inlet 326 andstationary blades 334 at the outlet 328. Permanent magnets 329 in thestator 320 and permanent magnets 331 in the impeller 322 support theimpeller 322 on one end. Permanent magnet 329 in the stator 320 andpermanent magnets 331 in the impeller 322 support the impeller 322 atthe outlet 328. A thrust bearing stator 346, coil 348 and thrust target348 a provide support in the axial direction. Power to rotate theimpeller is provided by a DC brushless motor consisting of an iron orother soft magnetic material, rotor ring 352, permanent magnets 354, anda stator coil 358. Blood pumped by the helical impeller blades 360accelerates the blood through the outlet 328.

Blood flow is partitioned into a primary path 362 and secondary pathsthrough component gaps 364, 366, 368 and 370, which define a continuousgap. The secondary blood flow paths serve the purpose of allowing fornon-contact support of the impeller. In order to ensure that blood flowsin the proper direction through the magnetic gaps, small blades orrifling may be added as shown at 372.

FIGS. 36 and 37 illustrate a centrifugal pump which is a variation ofthe embodiment shown in FIG. 34 where the outlet 400 is radial insteadof axial. The pump comprises a housing 402, an impeller 404, a stator406 means 408 for levitation and axially positioning the rotor and meansfor rotation 409. Also the thrust bearing is moved to lie downstreamfrom all other magnetic components, and the thrust bearing has apermanent magnet bias magnet 410. Fluid flow gap 412 provides for theprimary blood flow through the pump. A secondary fluid flow gap 414 alsoprovides blood flow therethrough; however, gap 414 is small such thatefficient levitation is provided. The anacronym for the embodiment shownin FIGS. 36 and 37 is represented by anacronym (11) above

While the present preferred embodiments and method of making the samehave been described herein, it is distinctly understood that theinvention is not limited thereto, but may be otherwise variouslyembodied with the scope of the following claims and any equivalentsthereof.

THE EMBODIMENT OF FIGS. 38-46

FIGS. 38-46 disclose another embodiment of a blood pump 500 of thisinvention. FIGS. 38-40 illustrate external views of the pump. Thisembodiment differs in several respects from the previous embodiments andis an improvement over the other embodiments described above. As shownin FIGS. 41 and 45, in this embodiment, the rotor 502 is magneticallysuspended between a stator 504 or stationary fixed support member, thatpreferably has stator blades, and a housing 506 and rotates about thestator 504. Further, the motor stator 508 that drives the rotor 502 ispreferably disposed within the housing 506, as shown in FIG. 41. Bydisposing the motor stator 508 within the housing 506 several advantagesare achieved. First, the heat generated by the motor stator 508 is moreeasily transferred away from the blood, as compared to when the motorstator 508 is disposed within the stator 504. As described above, byremoving the heat generated by the motor stator 508 away from the blood,it is easier to maintain the blood beneath a threshold temperature atwhich the blood tends to coagulate. This is significant in preventingthrombosis. Second, by placing the motor stator 508 within the housing506, the stator 504, including the stator's external surface area, canbe made smaller. By making the stator 504 smaller, the rotor 502including is external surface area can be made smaller. In addition, theinner surface 510 of the housing 506 along which blood flows can be madesmaller. By making the rotor 502, the stator 504 and the inner surface510 of the housing 506 smaller, the surface area of the pump 500 thatthe blood contacts can be made smaller. This decreases the likelihood ofthe blood being contaminated by contact with foreign surfaces and henceincreases the biocompatibility of the pump 500.

Some of the embodiments described above have similar features. Forexample, in the embodiment shown in FIGS. 1 and 30, the motor stator 508was disposed within the housing 506, but these embodiments do not have astator 504 about which the rotor 502 rotates. Further, the embodimentsof FIGS. 31 and 34 have a stator 504 about which the rotor 502 rotates,but in these embodiments the motor stator 508 that drives the rotor 502is disposed in the stator 504. Thus, while these other embodiments areimprovements, these embodiments suffer from the disadvantages describedabove.

The embodiment of the pump 500 of FIGS. 38-46 also has several otherinventive features including radial magnetic bearings, anelectromagnetic thrust bearing that operates with a controller and aposition sensor to control the axial position of the rotor and smoothconforming surfaces that form relatively smooth passageways for theblood to flow. Other inventive features of this embodiment are describedbelow.

1. The Motor and the Housing

In a preferred embodiment, the motor shown in FIGS. 41 and 42 is abrushless 2-pole DC motor. The motor stator 508 is disposed within thehousing 506 and preferably at the mid-section of the housing 506, sothat the motor stator 508 is aligned with the rotor 502. The inventionis not limited to this particular type of motor stator 508 and othertypes may be utilized, including, but not limited to slotted statormotors and motors with other numbers of poles. For example, a 4-polemotor may be employed and is beneficial because it produces a particularsymmetric magnetic field in the motor gap in spite of interference fromthe thrust bearing magnets. In the preferred embodiment shown, the motorstator 508 has 6 motor stator coils 514 that are toroidally wound aroundstator laminations 516. The stator laminations 516 are preferablymanufactured from relatively soft nickel alloy, but may be manufacturedfrom other suitable materials, including, but not limited to silicon orcobalt alloys. The motor stator 508 can be attached to the housing withany conventional fastening technique. In one embodiment, the motorstator 508 is bonded to the housing with a suitable adhesive.

Preferably, the motor stator 508 is an unslotted stator, so that themagnetic attractive force between the motor stator 508 and the rotor 502is decreased, relative to a slotted stator motor. The term motor stator520 used herein with respect to the embodiments of FIGS. 38-46 refers tothat portion of the motor around which the stator coils 514 are wound.The stator 504, as used herein with respect to the embodiment of FIGS.38-46, refers to the stationary portion of the pump around which therotor 502 rotates. Whether slotted or unslotted, the motor stator 508produces a magnetic force that attracts the rotor 502 to the motorstator 508 and away from the preferred position in which the rotor 502is suspended concentrically around the pump stator 504. In order toreduce the attractive force generated by the motor stator 508, the motorstator 508 is preferably unslotted. If the motor stator 508 was slotted,the motor stator 508 would have to be positioned further away from therotor 502 in order to reduce the attractive force exerted on the rotor502. This would increase the size of the pump 500 and thereby reduce thebiocompatibility of the pump 500. Alternatively, the magnetic bearingsthat radially suspend the rotor 502 would have to be larger, againthereby increasing the size of the pump 500 and decreasing thebiocompatibility of the pump 500.

In a preferred embodiment, the housing 506 is constructed from amaterial that has relatively low electromagnetic conductivity andpermeability properties. Further, the housing material preferably hasrelatively high electromagnetic resistivity. For example, non-ferrousmaterials such as ceramics, titanium and non-magnetic stainless steel,such as 303 stainless steel, are preferred. By manufacturing the housing506 from materials such as these, several benefits are obtained. First,because the housing 506 has relatively low electromagnetic conductivity,the eddy current losses within the housing are relatively small.Further, the low permeability of the housing increases the field inducedon the motor rotor by the motor stator. This enables the motor stator508 to be smaller, as compared to a similar pump that has a motor stator508 disposed within a housing 506 manufactured from a material that doesnot have the properties described above. The use of a smaller motorstator 508 enables the pump housing 506 and the overall size of the pumpto be made smaller. As described above, reducing the size of the pumphas biocompatibility advantages because the surface area of the pump 500in contact with the human body and the blood is thereby reduced.

The motor stator 508 interacts with a rotor motor magnet 521, shown inFIG. 41, to rotate the rotor and thereby pump blood. As is generallyknown, eddy current losses reduce the efficiency of an electromagneticmotor. These inefficiencies resulting from eddy current losses have theundesirable effect in blood pumps of having to increase the size of themotor stator 508 and thereby the pump 500. In order to minimize the eddycurrent losses, the rotor 502 may have an inner iron member 522, whichis also shown in FIG. 41, that forms part of the interior portion of therotor 502. This inner iron member 522 surrounds the fixed hub 524 of thestator 504 and thereby shields the fixed hub 524 from magnetic fieldsgenerated by the motor magnet 521 and the motor stator 508. Thisprevents or reduces the eddy current losses that would be formed frominteraction of the magnetic field generated by the motor stator 508, themotor magnet 521, and the permanent magnets of the fixed hub 524. Bypreventing or reducing the eddy current losses, the motor stator 508 andthe motor magnet 521 operate more efficiently and the size of the pump500 can thereby be minimized.

The housing may be formed from any number of sections, but in theembodiment shown in FIG. 41, the housing includes four sections, 506 a,506 b, 506 c, and 506 d. Sections 506 a and 506 d respectively definethe inlet and outlet of the pump and may have threads disposed along atleast a portion of their respective exteriors for installation purposes.Sections 506 a, 506 b and 506 c form the mid-section of the pump.Section 506 a is sealed to section 506 b and section 506 d with ano-ring 506 f and a groove 506 g, as are sections 506 b and 506 c,sections 506 c and 506 d. An electrical connector 506 h for powering themotor may travel through a section of the housing and in the preferredembodiment shown in FIG. 41, the connector 506 h travels through anaperture in section 506 d.

2. The Rotor and Stator

The embodiment of FIGS. 38-46 also has several other advantages. Forinstance, a smooth fluid passage, as shown in FIGS. 41 and 46, isdefined between the stator 504 and housing 506, the stator 504 and therotor 502 and the rotor 502 and the housing 506. As described below,this smooth passage of fluid is defined by the geometric relationshipsbetween the housing 506, the rotor 502 and the stator 504 and theminimizing of an relatively sharp protrusions or edges.

The embodiment showing in FIGS. 38-46 is similar to that described abovein that it includes a stator 504 that is coupled to the housing 506 atthe inlet 526 and outlet 528 of the pump 500. As used herein withrespect to the embodiment of FIGS. 38-46, the term stator 504 refers tothat stationary portion of the pump about which the rotor 502 rotates.The term stator 504 is not intended to necessarily include the motorstator 508. Rather, the term stator 504 refers to a stationary memberwhether or not it has a motor stator. In this embodiment, the stator504, as best understood with reference to FIGS. 41-43, preferably has afirst end 530, a second end 532 and a fixed hub support 524 thatconnects the first end 530 to the second end 532. The first end 530, asshown in FIGS. 40, 41, 43 and 44B, is preferably disposed at the inlet526 and has a plurality of stator blades 534 disposed about theperiphery of the first end 530. In the embodiment shown, the first end530 preferably has a substantially conically shaped nose, as shown inFIG. 43, so that blood can smoothly pass with minimal or no flowseparation over the first end 530 as the blood enters the pump 500. Thestator blades 534, shown in FIGS. 40, 41 and 44B, are disposed about thefirst end 530 and direct the blood flowing into the pump to the rotor502, as is described in further detail below. Since a portion of thefirst end 530 has a substantially conically shaped nose, this portion ofthe first end 530 has a varying diameter. However, the maximum diameterof the first end 530 is preferably d_(max1) as shown in FIG. 43 and isdisposed at the upstream end of the first end 530 of the stator 504.

As shown in FIG. 42, the fixed hub 524 extends from the first end 530 tothe second end 532. The rotor 502 is disposed about the fixed hub 524.The fixed hub 524 has a diameter d_(hub) as shown in FIG. 45.

The second end 532 of the stator 504 is also preferably substantiallyconically shaped, as shown in FIGS. 41, 43 and 44A, and has a pluralityof stator blades 536 disposed about its periphery. These stator blades536 direct the blood flowing from the rotor 502 to the outlet 528 of thepump 500. The second end 532 of the stator 504 is also mechanicallycoupled to the housing 506. Because the second end 532 of the stator 504is substantially conically shaped, the blood flowing over the second end532 of the stator 504 can smoothly pass from the stator 504 to theoutlet of the pump 500.

The second end 532 of the stator 504 is connected to the fixed hub 524,and because the second end 532 is substantially conically shaped it hasa varying diameter. The maximum diameter of the second end 532 of thestator d_(max2) is disposed proximate to the fixed hub 524, as bestunderstood with reference to FIGS. 41 and 43. The fixed hub 524 may beconnected to the first end 530 and the second end 532 by any of avariety of mechanical fastening techniques. In the preferred embodimentshown, the fixed hub 524 is connected to the first end and the secondend with a pin 524 a and a bushing guide 524 b respectively. The pin 524a and the bushing guide 524 b of the respective end of the fixed hub 524connect the fixed hub 524 to the first end 530 through an interferencefit and the fixed hub 524 to the second end 532 with an interferencefit.

The rotor 502 is preferably disposed about the fixed hub 524, as shownin FIGS. 41 and 43, and has a substantially cylindrically shaped portion538 and a substantially conically shaped portion 540. The rotor 502preferably has an annular cross-section that is disk shaped. Asdescribed in more detail below, the rotor 502 is magnetically suspendedabout the fixed hub 524, and rotor blades 542 extend from thesubstantially conically shaped portion 540 to the substantiallycylindrically shaped portion 538. When disposed about the fixed hub 524,the outer periphery of the substantially cylindrical portion 538 of therotor 502 has a diameter d_(rotor), as shown in FIG. 43. Preferably, thed_(rotor) is approximately equal to the d_(max2) of the second end 532of the stator 504, so that a smooth passage of blood from the rotor 502to the second end 532 of the stator 504 takes place as the blood passesthrough the pump.

By shaping and sizing the stator 504 and the rotor 502 as describedabove, relatively smooth surfaces are created that decrease thelikelihood of the activation of platelets, coagulation and thrombosis.If the rotor 502 was not suspended so that the diameter of the rotord_(rotor) approximately equaled the diameter d_(max2) of the second endof the stator 504, a rather abrupt transition would be created betweenthe rotor 502 and the stator 504 that would increase the likelihood ofdamage to the blood cells.

The relatively smooth surfaces that prevent damage to the blood alsoinclude the substantially conically shaped first end 530 of the stator504. The first end 530 of the stator 504 creates a relatively smoothsurface that the blood contacts upon entering the pump so that shearstresses are minimized as the blood flow is redirected. This conicallyshaped relatively smooth surface of the first end 530 also directs theblood to flow to the substantially conically shaped section 540 of therotor 502. Because the rotor 502 and part of the second end of thestator 504 have about the same diameter, a relatively smooth passage iscreated from which the blood can flow from the rotor 502 to the secondend of the stator 504. After flowing to the second end of the stator504, the substantially conically shaped second end 532 of the stator 504provides a relatively smooth surface over which the blood flows, as theblood is redirected to the outlet of the pump 500 and from a largerdiameter section to a smaller diameter section.

As alluded to above, the housing 506 encloses the rotor 502 and thestator 504. The housing 506 preferably has an inner surface 510, asshown in FIG. 41, that extends from the inlet 526 of the pump to theoutlet 528 of the pump. As is described in further detail below, aprimary flow path is defined between the housing 506 and the rotor 502and the housing 506 and the stator 504. The inner surface 510 preferablyhas a shape that conforms to the shape of various parts of the rotor 502and the stator 504, so that the primary flow path defined between thestator 504 and the rotor 502 is relatively smooth, and the blood flowexperiences relatively minor changes in cross-sectional areas in theflow path. As described above, it is important in the design of bloodpumps that relatively sharp protrusions and edges be avoided becausethey can cause shear stresses in the blood and create localized regionsof stagnation in which the blood may coagulate.

One of the ways the pump 500 of this invention avoids having edges andrelatively sharp protrusions is by having an inner surface 510 of thehousing 506 that conforms to the shape of portions of the stator 504 andthe rotor 502. For example, the inner surface 510 of the housing 506 hasa first portion 542 that is curved along the substantially conicallyshaped portion 540 of the rotor 502 to create a relatively smoothpassage of blood between the rotor 502 and the housing 506. This isparticularly important in this region of the pump 500 because the rotorblades 542 on the substantially conically shaped portion 540 of therotor 502 are imparting energy to the blood and the blood is beingredirected from flowing in a substantially axial direction to an angulardirection that is an angular relationship with the longitudinal axis ofthe pump. Redirecting the direction of flow of the blood and the pumpingaction of the impeller blades 542 has the potential to cause shearstresses on the blood. In order to reduce the likelihood of damage tothe blood cells, the inner surface 510 of the housing 506 is curved toconform to the substantially conically shaped section of the rotor 502.This provides a relatively smooth redirection of the blood as the bloodis pumped and flows between the substantially conically shaped section540 of the rotor 502 and the inner surface 510 of the housing 506.

The inner surface 510 of the housing 506 also has a second portion 546that is disposed proximate to the substantially cylindrical shapedsection of the rotor 502. This second portion 546 of the housing 506 ispreferably substantially cylindrically shaped, so as to conform to theshape of the substantially cylindrically shaped section 538 of the rotor502. This creates a relatively smooth passage of flow between thesubstantially cylindrical portion 538 of the rotor and the inner surface510 of the housing 506. As discussed above, the creation of a relativelysmooth flow passage minimizes the shear stresses and the likelihood ofdamage to the blood cells.

A third portion 548 of the inner surface 510 of the housing 506preferably extends from the second portion 546 of the inner surface 510of the housing 506 and is disposed proximate to the substantiallyconically shaped second end 532 of the stator 504. Similar to the firstportion 540 of the inner surface 510 of the housing 506, the thirdportion 548 of the inner surface 510 of the housing 506 conforms to thesubstantially conically shaped second end 532 of the stator 504 tocreate a relatively smooth flow passage between these two surfaces.While flowing between the substantially conically shaped second end 532of the stator 504 and the third portion 538 of the inner surface 510 ofthe housing 506, the flow is being redirected from the axial directionto a direction that is an angular relationship with the axial direction.Additionally, the flow is being straightened by the stator blades 536.One of the primary concerns with blood flowing between the stator andthe housing is preventing flow separation, flow reversal, stagnation andthrombosis that can result from these phenomena. In order to reduce thelikelihood of flow stagnation, flow reversal and thrombosis, theconforming surfaces of the pump define a relatively smooth flow passagebetween the stator and the housing.

By configuring the pump as described above, the blood pump is a mixedflow pump. A mixed flow pump being one that combines the characteristicsof both axial and centrifugal pumps. As is generally known, axial pumpshave a fluid entering along an axis and the general direction of fluidflow is parallel to this axis through the pump. Centrifugal pumpsgenerally have a fluid entering in the pump in a direction that isgenerally parallel to the axis of symmetry of the pump rotor and exitingthe pump in a direction that is generally perpendicular to the directionat which the flow enters the pump. A mixed flow pump combines thecharacteristics of these pumps and has flow in a direction other thanthe general direction of flow as defined in these types of pumps. Forexample, as shown in FIG. 45, the flow enters the pump in generally theaxial direction and then is diverted to an angular direction with thelongitudinal axis of the pump, as the blood passes the substantiallyconically shaped section 540 of the rotor 502. After which, the flowreturns to is generally axial direction as the blood passes along thesubstantially cylindrical portion 538 of the rotor 502. After flowingpast the substantially cylindrical portion 538, the blood begins in anangular direction again along the substantially conically shaped secondend 532 of the stator 504. Following this, the flow again is redirectedto the axial direction as the blood exits the pump.

Blood pumps generally operate under what are regarded as intermediateflow and pressure conditions. At these conditions, a mixed flow pump ismore efficient and therefore preferred over centrifugal and axial pumps.As is generally known, axial flow pumps are preferred in applicationsinvolving relatively low pressures and high flow rates, and centrifugalflow pumps are preferred in applications involving relatively highpressures and low flow rates. Thus, by providing a mixed flow pump, thisinvention provides a pump that operates most efficiently for itsapplication. Further, the mixed flow design conveniently accommodatesthe required diameter increase necessary to house the rotor and stator.

As described above, increasing the efficiency of the pump permits thepump to be smaller and thereby enhances its biocompatability. Forexample, the pressure is generated predominately by the substantiallyconical shaped portion 540 as the rotor 502. By generating a significantportion of the pressure in this section of the pump, the substantiallycylindrically shaped portion 538 of the rotor 502 can be made relativelysmaller which permits the size of the primary flow path across which themotor operates to be smaller and thereby increases the efficiency of thepump. In contrast, if the pump was axial in design, the size of therotor and the motor would have to be larger to obtain the same operatingconditions. Although this preferred embodiment has been described interms of a mixed flow pump, this is not intended to limit theapplication of other features of the pump to mixed flow pumps exceptwhere expressly stated. This invention includes pumps with a housing inwhich a motor is disposed and that has a rotor that rotates about aninner stator that are not mixed flow pumps. In a preferred embodiment,the pressure rise between the conical portion of the rotor and thehousing is in the range of about 80-140 mm. Hg at a flow rate of about 3to 10 liters/min.

The pump of FIGS. 38-46 can be described in terms of the acronymsdescribed above. Using these terms, the pump is described as follows:

The ATB and PRB are hybridized in this embodiment because the aftbearing outer race shares magnets with the active thrust bearing. Thishybridization need not be used and separate magnets may be used.However, by hybridizing, fewer parts are used which providesmanufacturing and economic advantages.

3. The Flow Paths

Similar to some of the embodiments described above, the pump of FIGS.38-46 has two flow paths, as are best shown in FIG. 45. There is aprimary flow path 550 between the rotor 502 and the housing 506 and asecondary flow path 552 between the rotor 502 and the stator 504, as isbest shown in FIG. 45. The primary flow path 550 is larger than thesecondary flow path 552, and the majority of blood passing through thepump flows through the primary flow path 550. The secondary flow path552 is necessitated by the use of magnetic bearings which permit therotor 502 to levitate. The creation of a secondary flow path 552 acrosswhich the magnetic bearings communicate with the rotor to suspend therotor 502 is significant because without a secondary flow path 552, themagnetic bearings must work across the primary or only flow path in thepump. Because magnetic bearings need to be relatively close together inorder to be efficient, without a secondary flow path the rotor wouldhave to be disposed relatively close to a housing and the size of theflow path would be limited and therefore, the flow rate would belimited. Thus, the creation of a secondary flow path permits themagnetic suspension of a rotor without limiting the size of the primaryflow path and the flow rate. The size of the flow path could beincreased by using larger bearings in lieu of a secondary flow path, butthis would increase the size of the pump and cause the biocompatibilitydisadvantages alluded to above.

The dimensions of the secondary flow path 552 are important for both theoperation and the hemo-compatibility of the pump 500. If the secondaryflow path 552 is too small, the magnitude of the shear stresses on theblood from the relatively small flow path can become excessive andresult in damage to the red blood cells, coagulation and thrombosis.Conversely, if the secondary flow path 552 is too large, the rotor 502will be disposed farther away from the stator 504. This increaseddistance results in less efficient magnetic bearings and causes themagnetic bearings to be larger in order to generate the same magneticforce. This can result in an increase in pump size which has thebiocompatibility disadvantages discussed above. Furthermore, if thesecondary flow path is too large, it will provide excessive flushing orleakage losses which degrade the hydrodynamic efficiency of the pump andcause undesirable flow disturbances at the interfaces of the primary andsecondary flow paths. In a preferred embodiment of this invention, thedistance between the stator 504 and the rotor 502 is within the range ofabout 0.005 ins. to about 0.03 ins. Of course, the preferred size of thesecondary flow path 552 will depend on the overall size of the pump 500.Further, the preferred distance from the exterior of the rotor to thehousing that determines the primary flow path is about 0.0495 ins. Whatis important is that the secondary flow path 552 is large enough toprevent excessive shear stresses, yet small enough to prevent theefficiency of the bearings from being decreased and the overall size ofthe pump 500 from having to be thereby increased.

As referenced above, the flow in the secondary flow path 552 ispreferably from the downstream end 554 of the secondary flow path 552through the secondary flow path 552 and out the upstream end 556 of thesecondary flow path 552. In other words, the flow through the secondaryflow path is retrograde and opposes the flow in the primary flow path550. This embodiment of the pump 500 was designed with retrograde flowbetween the rotor 502 and the stator 504 in order to increase theflushing of the secondary flow path 552. In order to design amagnetically suspended rotor 502 about a stator 504, it has been foundthat the secondary flow path 552 must be of a requisite size in orderfor the magnetic bearings to be efficient and in order to preventexcessive shear stresses. Another concern with a secondary flow path 552is to ensure that the flow rate through the secondary flow path 552 issufficient to provide adequate flushing and prevent regions ofstagnation and the coagulation of platelets that can result fromstagnation. Through design and experimentation, it has been found thatit is difficult to prevent stagnation and provide adequate flushing whenthe flow in the secondary flow path 552 is in the same direction as theflow in the primary flow path 550. For example, the size of thesecondary flow path 552 would have to be increased which has thedisadvantages described above. Thus, in a preferred embodiment the pump500 has been designed with retrograde flow through the secondary flowpath 552 to provide adequate, but not excessive, flushing and therebymaintain the size of the secondary flow path 552 relatively small.

4. The Blades

Disposed on the rotor 502 are preferably a plurality of rotor blades542, as best shown in FIG. 43. These rotor blades 542 extend from thesubstantially conically shaped portion 540 of the rotor 502 onto thesubstantially cylindrical portion 538 of the rotor 502. Preferably, therotor blades 542 are curved or wrapped in a substantially helicalpattern about the substantially cylindrical portion 538 of the rotor502. Upon reaching the cylindrical portion 538 of the rotor 502, thecurvature (wrap) of the rotor blades 542 decreases, as is best shown, inFIG. 43.

This curvature (wrap) is preferable for a variety of reasons. Thefunction of the helical curved blades 542 on the conically shaped end540 of the rotor 502 is primarily to impart pressure energy, rotationalvelocity and axial velocity to the blood. In contrast, the primaryfunctions of the portion of the blades 542 on the substantiallycylindrical portion 538 of the rotor 502 is to impart further rotationalkinetic energy to the blood and serve as a guide to direct the flow ofblood toward the leading edge of the stator blades disposed at thesecond end 532 of the stator 504.

Each rotor blade 542 has a tip 556 and a root 558, one of which is shownin FIG. 43. The tip 556 of each rotor blade 542 is preferably rounded.Similarly, each blade 556 has a fillet 560 disposed in either side ofthe root 558 of each blade 542 where the root 558 contacts theperipheral surface of the rotor 502. By rounding the tip 556 andproviding fillets 560 at the root 558 of each blade 542, the relativelysharp edges associated with flat tips and roots that mate with a surfaceat right angles are generally eliminated. The elimination of theserelatively sharp edges is advantageous because the sharp edges can causeshear stresses within the blood and non-filleted intersections can causelocalized regions of relatively stagnant blood. This may result incoagulation or thrombosis. Therefore, the rounding of the tip 556 andthe creation of fillets 560 at the root 558 of the blades 542 along thelength of the respective blade 542 reduces the shear stresses andproblems associated with the shear stresses. In a preferred embodiment,the blades are curved at a curvature that is approximately within therange of about 0.002 ins. to about half of the width of the blade.

The stator blades 536 disposed on the second end 532 of the stator 504preferably have a reverse spiral curvature, as shown in FIGS. 43 and44A. Because of this curvature (wrap), the stator blades 536 straightenthe flow, as the blood exits the pump 500, and reduce the rotationalkinetic energy of the blood in the circumferential direction and therebyrecover pressure energy from the blood. The thickness of the blades aredesigned so as to minimize axial variations in the flow path's crosssectional area. This minimizes the potential for flow separation fromthe hub and the blades, which reduces the likelihood of blood damage.

In the embodiment shown in FIGS. 43 and 44A the stator blades 536 on thesecond end of the stator having a changing thickness in order to keepthe net cross-sectional area of the flow path constant and therebyprevent flow separation. For instance, as the shape of the housingchanges proximal to the stator blades 536, the stator blade thickness isadjusted to maintain the cross-sectional area relatively constant. Asthe shape of the housing tends to increase the size of the flow path,the thickness of the stator blades is increased to maintain thecross-sectional area of the flow path relatively constant.

5. The Magnetic Bearings

As alluded to above, the pump of FIGS. 38-46 also has magnetic bearingsthat magnetically suspend and position the rotor 502 radially andaxially between the housing 506 and the stator 504. A preferredembodiment of a radial magnetic bearing 560 and a thrust bearing 562 isprovided below, but other magnetic bearings may be utilized. In theembodiment provided below, the radial magnetic bearing 560 is a passivebearing, and the thrust bearing 562 is an active bearing that senses theposition of the rotor 502 during the operation of the pump and providesan axial force to the rotor 502 to position the rotor 502 axially withinthe pump.

In the embodiment shown in FIGS. 38-46, two radial bearings 560 areprovided. Both sets of radial bearings 560 include a stack of permanentmagnets disposed within the stator 504 and a stack of permanent magnetsdisposed with the rotor 502, as shown diagrammatically in FIG. 46. Thesestacks of permanent magnets include the rotor aft stack 564, the rotorforward stack 566, the stator aft stack 568 and the stator forward stack569. The arrows in the FIG. 46 indicate the direction of the magneticfield produced by a particular component. The arrow head indicates northand the tail indicates south.

The rotor aft stack 564 of permanent magnets includes, in a preferredembodiment, three magnets 570, 572, 574. The combination of these threemagnets forms what is referred to as an aft outer race. They arereferred to as an outer race because each of the permanent magnets 570,572, 574 is shaped in the form of a ring. Preferably, the rotor magnetsof the aft stack 564 or race are magnetized in alternating directions asshown in FIG. 46. Preferably, the aft rotor stack 564 of permanentmagnets also includes two thrust poles 582, 584 which form part of thethrust bearing 562, as described in detail below. Aligned with the aftrotor stack 564 of permanent magnets may be the aft stator stack 568 ofpermanent magnets. Similar to the rotor aft stack 564, the stator aftstack 568 includes three permanent magnets 576, 578, 580. The aft statorstack 568 also includes a spacer 575 disposed between two of the threeafter stator stack magnets. The magnets that define the aft stator stack568 are also preferably shaped in rings and together are referred to asthe aft inner race.

Similarly, the forward rotor stack 566 of permanent magnets includes ina preferred embodiment three permanent magnets 586, 588, 590 that definethe forward outer race. These magnets are preferably magnetized inalternating directions, as shown in FIG. 46, and in alternatingdirections from those magnets that define the aft outer race 564. Thestator forward stack 569 also includes three magnets 592, 594, 596 ofalternating polarity from each other and the magnets that define the aftstator magnets. The forward stack 569 of stator magnets defines theforward inner race.

Together the aft outer 564 and inner races 568 define an aft radialbearing and the forward outer 566 and inner races 569 define a forwardradial bearing. Each of these bearings communicates magnetically acrossthe secondary flow path 552 that separates the rotor 502 from the fixedhub 524 to magnetically suspend the rotor 502 from the stator 504, asshown in FIG. 41. The size of the secondary flow path 552 or gap acrosswhich the respective inner and outer races must communicate with eachother is important for the proper operation of the pump. As describedabove, the gap must be small enough to provide for efficienttransmission of magnetic force in the radial direction to levitate thepump, so that the bearings and pump size can be minimized, yet not sosmall as to cause excessive shear stresses on the blood. A preferredsize of this gap is provided above.

The forward radial bearing defined by the forward outer race 566 and theforward inner race 569 is similar to other magnetic bearing constructionsuch as that described in Backers, FT “A Magnetic Journal Bearing,”Phillips Technical Review, Vol. 22, pp. 323-328 (1960-61) and Yonnet J.P., et al. “Stacked Structures of Passive Magnet Bearings,” J. Appl.Physics 70(10):6633-6635 (1991). A preferred embodiment of a radialmagnetic bearing that magnetically suspends the rotor 502 about thestator 504 has been provided above. However, other magnetic bearingsconfigurations are possible. For example, a different number of magnetsmay be used and/or different polarity of magnets may be used. Further,active magnetic bearings may also be used.

Because of the position of the rotor motor magnet 521 relative to theforward radial magnetic bearing, the forward inner race 569 has thepotential to interact magnetically with the rotor motor magnet 521. Forexample, the motor stator 508 can create a dipole moment that interactswith a dipole moment created by the inner race magnets. This interactionwould produce an undesirable moment on the rotor 502 in the pitch andyaw directions that bends the rotor 502 away from its preferredsuspended position between the stator 504 and the housing 506. In orderto prevent this undesirable bending moment, the thicknesses of the outermagnets 586, 590 that define the forward inner race are adjusted untilthe moment generated by the forward inner race 569 is approximatelyzero. This nullifies and minimizes any interaction between the rotormotor magnet 521 and the forward inner race 569 and thereby prevents orminimizes the undesirable bending moment that results from theinteraction. In a preferred embodiment the thicknesses t₁ and t₂ of themagnets that define the forward magnetic bearing about twice thedistance between the inner and outer races or twice the size of thesecondary flow path. The overall length of the stack of magnets ispreferably shown so as to achieve sufficient stiffness to support therotor while its rotating. Likewise the thicknesses t_(3 and) t₄ of twoof the magnets that define the forward inner race 569 are adjusted tomatch the thicknesses t₁ and t₂ of the corresponding outer magnets.

In order to position the rotor 502 axially within the housing, the pumpmust also have a thrust bearing 562. Preferably, the thrust bearing 562is an active magnetic bearing that adjusts the axial force on the rotor502 to maintain the proper position of the rotor 502. In a preferredembodiment, the thrust bearing 562 includes the aft outer race 564, apair of thrust poles 582, 584, a pair of thrust coils 598, 600. positionsensors 602. 604 and a controller 620 that controls the force exerted onthe rotor 502 in response to the position sensors 602.

As described above, the aft outer race 564 and the thrust poles 582, 584are positioned within the rotor 502, and the aft inner race 568 isdisposed within the stator 504. The thrust coils 598, 600 areelectromagnetic coils that are disposed within the housing 506, as shownin FIG. 41. In a preferred embodiment, one of the thrust poles 582 is anorth pole and the other is a south pole. Thrust coil 598 preferablyinteracts with thrust pole 582, and thrust coil 600 preferably interactswith thrust pole 584. The electrical currents through the thrust coils598, 600 are preferably counter rotating, so that they each interactwith the respective thrust poles 582, 584 to produce an axial force inthe same direction. The magnetic field generated by the aft inner 564and outer 568 races interacts with the magnetic field generated by thethrust coils 598, 600 and the thrust poles 582, 584 to provide an axialforce that positions the rotor 502 axially within the housing 506.

Position sensing coils 602, 604 shown in FIG. 41, are preferablydisposed within the second end of the stator 504 and at the stator face606. The sensing coils 602, 604 may be of the eddy current type, butother suitable sensors may be used.

In order to properly position the rotor 502 axially, a controller thatcontrols the current through the thrust coils is disposed. In apreferred embodiment, the controller is a conventional feedbackcontroller, such as that described above, that is responsive to thesensing coils 602, 604 to position the rotor axially. The sensing coilssend an electrical signal to the controller that is indicative of theaxial position of the rotor. The controller adjusts the current in thethrust coils to reposition the rotor in the preferred axial position.

In an alternative preferred embodiment, a Virtually Zero Power (VZP)controller 620, shown schematically in FIG. 46, is used with thefeedback controller. The VZP controller positions the rotor 12 at thezero velocity point along the axial axis of the pump. The zero velocitypoint is an unstable equilibrium point where static loads and unstableforces produced by the radial bearings are balanced and a net force ofzero is produced. An advantage of employing a VZP controller is that thepower required to maintain this position, assuming no externaldisturbances, is about equal to the quiescent power of the controller'selectronics, and therefore is relatively small.

In operation the sensing coils 602, 604 measure the position of therotor and conventional position feedback is used to suspend the rotorinitially. After a stable suspension of the rotor is achieved, the VZPcontroller 620 maintains the position of the rotor.

The VZP controller can be of the type that uses velocity feedback toposition the rotor at the zero velocity point and is described generallyin Carl H. Henriksoti, Joseph Lyman, and Philip A. Studer,: MagneticallySuspended Momentum Wheels For Spacecraft Stabilization, presented at theAIAA 12th Aerospace Sciences Meeting, Washington D.C. Jan. 30-Feb. 1,1974 and available as AIAA Paper No. 74-128, p. 4-5 (1974) and JosephLyman: Virtually Zero Powered Magnetic Suspension, U.S. Letters Pat. No.3,860,300, Jan. 14, 1975, which are both hereby incorporated byreference. Alternatively, the VZP controller can be of the type thatuses integral feedback of a signal that is a function of the current inthe thrust coils 598, 600. This type of controller is described in BallBrothers Research Corp.: Annular Momentum Control Device (AMCD), VolumeI: Laboratory Model Development, NASA CR-144917, pp. 4-6-4-9, (1976),which is hereby incorporated by reference. In either type, the preferredposition is the zero velocity position.

Various inventive features of a blood pump of this invention have beendescribed above. It will be appreciated that not all inventive featuresneed be combined in a single pump. Rather, some inventive features maybe included within other pumps without using other inventive features.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

What is claimed is:
 1. A pump for pumping blood, comprising: a housing;a stator disposed within the housing and coupled to the housing; a rotordisposed within the housing and suspended around the stator; the rotorand stator defining a primary blood flow path between the rotor and thehousing and a secondary blood flow path between the rotor and thestator; at least two radial magnetic bearings for suspending the rotorbetween the stator and the housing, said radial magnetic bearings eachcomprising at least one stator suspension magnet disposed within thestator and at least one rotor suspension magnet disposed within therotor, the stator and rotor suspension magnets communicating across thesecondary flow path; and a motor for rotating the rotor with respect tothe stator, said motor comprising at least one electromagnetic coilwithin the housing, said electromagnetic coil communicating with atleast one rotor motor magnet in the rotor, said communication beingacross the primary flow path to rotate the rotor with respect to thestator and thereby pump blood through the pump.
 2. The blood pump ofclaim 1, wherein the stator further comprises a first end disposed at aninlet of the pump, a second end disposed at an outlet of the pump and afixed hub that connects the first end to the second end.
 3. The bloodpump of claim 2, wherein the stator further comprises a plurality ofstator blades extending from the first end of the stator and a pluralityof stator blades extending from the second end of the stator.
 4. Theblood pump of claim 1, wherein the motor comprises an unslotted motorstator, disposed in the housing.
 5. The blood pump of claim 1, whereinthe housing comprises a material of relatively low electro-thermalconductivity.
 6. The blood pump of claim 1, wherein the housingcomprises a ceramic material.
 7. The blood pump of claim 1, wherein thehousing comprises non-magnetic stainless steel.
 8. The blood pump ofclaim 1, wherein the rotor motor magnet comprises a permanent magnet forinteracting with the electromagnetic coil.
 9. The blood pump of claim 1,wherein one of the stator suspension magnets has a thickness thatreduces the magnetic interaction between the respective statorsuspension magnet and the motor magnet to reduce a moment, created bythe interaction of the motor magnet and the stator suspension magnet,that biases the rotor from a preferred suspended position.
 10. The bloodpump of claim 1, wherein the rotor magnet comprises a plurality of ringshaped magnets of alternating polarities and the stator magnet comprisesa plurality of ring shaped magnets of alternating polarities.
 11. Theblood pump of claim 1, further comprising thrust coils, disposed withinthe housing and thrust poles, disposed within the rotor, one of thethrust coils interacting with one of the thrust poles and the other ofthe thrust coils interacting with the other of the thrust poles toposition the rotor axially within the housing.
 12. The blood pump ofclaim 11, further comprising at least one sensing coil, disposed withinthe stator, that senses the axial position of the rotor.
 13. The bloodpump of claim 12, further comprising a controller, that interacts withthe thrust coils to control an electrical current through the thrustcoils in response to the at least one sensing coil so that the thrustcoils apply an axial force on the rotor to position the rotor axiallywithin the housing.
 14. A system for pumping blood, comprising: (i) apump, comprising: a housing that has an inlet and an outlet; a statordisposed within the housing and having a first end, disposed at theinlet, about which a plurality of stator blades are disposed, a secondend, disposed at the outlet, about which a plurality of stator bladesare disposed and a stationary hub that connects the first end to thesecond end; a rotor, suspended between the stationary hub and thehousing; a first radial magnet bearing defined by a first set of magnetsof alternating polarity, disposed within the rotor, that define an outerrace and a second set of magnets of alternating polarity, disposedwithin the stator stationary hub, that define an inner race, the innerrace and the outer race communicating across a gap between thestationary hub and the rotor to suspend the rotor about the stationaryhub; a thrust bearing defined by a pair of thrust coils, disposed withinthe housing, and a pair of magnetic poles, disposed within the rotor,each of the thrust coils interacting with one of the magnetic poles toproduce an axial force on the rotor to position the rotor axially withinthe housing; a sensing coil, disposed within the stator, that senses theaxial position of the rotor; and (ii) a controller, coupled to thesensing coil of the pump that controls an electrical current flowingthrough the thrust coils to produce a correcting force that positionsthe rotor axially in response to the position sensed by the sensingcoil.
 15. The system pump of claim 14, wherein the pump furthercomprises a second radial magnetic bearing that further comprises athird set of magnets of alternating polarity, disposed within the rotor,and a fourth set of magnets of alternative polarity, disposed within thestator, the third set of alternating magnets and the fourth set ofalternating magnets interacting across the gap to define a second radialbearing.
 16. The system of claim 14, wherein the pump further comprisesa motor, disposed within the housing that communicates with a motormagnet, disposed within the rotor, to rotate the rotor.
 17. The systemof claim 16, wherein a thickness of the first set of alternating magnetsis such that the magnetic interface between the motor magnet and thefirst set of alternating magnets does not produce an undesirable bendingmoment on the rotor.
 18. The system of claim 14, wherein the controllercomprises a virtual zero power controller.
 19. A pump for pumping blood,comprising: a housing that has an inlet and an outlet; a stator,disposed within the housing, and having a first end, that is coupled tothe housing proximate to the inlet and a second end, that is coupled tothe housing proximate to the outlet; a rotor, magnetically suspendedbetween the stator and the housing; a radial magnetic bearing thatincludes a rotor magnet, disposed within the rotor, and a stator magnet,disposed within the stator and aligned with the rotor magnet, theinteraction of the rotor magnet and the stator magnet suspending therotor radially between the housing and the stator; a primary flow pathdefined between the rotor and the housing; a secondary flow path definedbetween the rotor and the stator, the secondary flow path being largeenough to provide adequate flushing of the secondary flow path and smallenough so that the rotor magnet and the stator magnet can interface tosuspend the rotor radially.
 20. The pump of claim 19, wherein the flowthrough the secondary flow path is in a direction that is opposite theflow through the primary flow path.
 21. The pump of claim 19, whereinthe secondary flow path comprises an entrance disposed between thesecond end of the stator and the rotor, a substantially inward radialflow path defined between the second end of the stator and the rotor, asubstantially axial flow path defined between the stator and the rotorand an exit, defined between the stator and the rotor.
 22. The pump ofclaim 19, further comprising a magnetic thrust bearing for axiallyaligning the rotor within the housing.
 23. The pump of claim 22, whereinthe magnetic thrust bearing comprises an active magnetic bearing. 24.The pump of claim 23, wherein the active magnetic thrust bearingcomprises a pair of thrust coils, disposed within the housing, that eachinteract with one of a pair of poles, disposed within the rotor, toplace an axial force on the rotor.
 25. The pump of claim 24, wherein theactive thrust bearing further comprises a sensor, disposed within thestator, for sensing the axial position of the rotor, and anelectromagnetic controller, disposed within the pump, that controls theelectrical current flowing through the thrust coils to position therotor axially within the housing.